Cerussite is lead carbonate (PbCO3). It has a nonmetallic luster and is typically clearish to whitish to grayish. It is noticeably heavy for its size, due to the lead content. Cerussite is a secondary mineral - it forms as an alteration product of galena. Naturally-occurring acidic fluids that attack galena cause it to convert to other minerals, particularly anglesite (lead sulfate) and cerussite (lead carbonate). Partially altered galenas often show galena at the core, surrounded by anglesite, with good cerussite crystals growing atop the anglesite.
Cerussite (field of view ~2.7 cm across) - clear cerussite crystals on matrix of galena (PbS), from the Toussit Mine, south of Oujda, Atlas Mountains, far-northeastern Morocco.